Apparatus for detecting position of reference pattern

Abstract

An apparatus for detecting a position of a reference pattern or mark formed in a substrate to be aligned with a photomask pattern performs the following functions: scanning a reference pattern having at least two edges and generating a time-serial pattern signal corresponding to the scanned pattern; extracting all scanning positions at which a waveform of the pattern signal has a shape corresponding to an edge of the pattern within a predetermined scanning range including the pattern; selecting one pair from all possible pairs of a plurality of extracted scanning positions in accordance with a degree to which a pattern signal between the two scanning positions defined by each pair satisfies predetermined waveform conditions; and determining as a pattern position a predetermined position at which the interval between the two scanning positions of the selected pair is divided into two intervals by a predetermined ratio.

We claim: 
     
       1. An apparatus for detecting a position of a substrate on which a reference pattern is formed, the reference pattern having at least two opposing edges and a plurality of grating elements arranged at a predetermined pitch along the two edges, comprising: means for supplying a spot of a light beam onto said substrate;   means for scanning the reference pattern by said spot along a scanning line crossing the two edges;   means for receiving a part of the light beam diffracted by said edges and generating a time-serial output signal corresponding to the reference pattern on the scanning line, the output signal having an output waveform including two bottom portions respectively corresponding to the two edges and a peak between the bottom portions;   means for amplifying the output signal and having a nonlinear amplification characteristic wherein a gain at the bottom portions is larger than that at the peak;   means for adjusting said amplification characteristic on the basis of an evaluation of the output waveform; and   means for detecting the position of the reference pattern with respect to the scanning line from the output signal amplified by said amplifying means, wherein said position is determined at the center of the interval between said two bottom portions.   
     
     
       2. An apparatus according to claim 1, wherein said adjusting means determines said amplification characteristic on the basis of an amount of the peak of the output waveform. 
     
     
       3. An apparatus according to claim 1, wherein said adjusting means determines said amplification characteristic on the basis of the distortion of the output waveform. 
     
     
       4. An apparatus for detecting a position of a substrate on which a reference pattern is formed, the reference pattern having at least two opposing edges and a plurality of grating elements arranged at a predetermined pitch along the two edges, comprising: means for supplying a spot of a light beam onto said substrate;   means for scanning the reference pattern by said spot along a scanning line crossing the two edges;   means for receiving a part of the light beam diffracted by said edges and generating a time-serial output signal corresponding to the reference pattern on the scanning line, the output signal having an output waveform including two bottom portions respectively corresponding to the two edges and a peak between the bottom portions;   means for digitizing the output signal at a threshold level corresponding to said bottom portions of the output waveform;   means for adjusting said threshold level on the basis of the output waveform; and   means for detecting the position of the reference pattern with respect to the scanning line from the output signal digitized by said digitizing means, wherein said position is determined at the center of the interval between said two bottom portions.   
     
     
       5. An apparatus according to claim 4, wherein said adjusting means determines said threshold level on the basis of an amount of the peak of the output waveform. 
     
     
       6. An apparatus according to claim 4, wherein said adjusting means determines said threshold level on the basis of the distortion of the output waveform. 
     
     
       7. An apparatus according to claim 4, wherein said scanning means includes means for oscillating said spot at a predetermined period; said receiving means generates the output signal modulated by the oscillation period of the spot; and said detecting means includes means for demodulating the digitized output signal at the oscillation period and for generating a detection signal corresponding to a positional deviation between an oscillation center of the light beam and the reference pattern.